(1) Field of the Invention
The present invention relates to touch sensor controls including touch input systems (touch screens used in fixed or mobile devices, such as point of sales terminals, kiosks, laptops, monitors, POS, POI, PDAs, cell phones, UMPCs and the like). More particularly, the invention relates to touch sensor controls having both a touch-coordinate calculation ability as well as a force sensing ability.
(2) Description of Prior Art
The concept of using multiple force sensing sensors to register, measure and triangulate the touched position of a touch screen has been a known concept for more than twenty years, however, to produce a high quality touch screen solution has proven difficult.
Over the last few years the performance trade-offs of the available force sensing technologies has fragmented the market. There are approximately ten (10) different touch screen technologies. However, only one such technology has been adapted to measure both the touch coordinates as well as the absolute amount of touch force. This is “force-based touch screen technology” as described in U.S. patent application Ser. Nos. 13/425,846; 12/450,138; PCT/US2008/003374; and F-Origin's zTouch™ at www.f-origin.com. The other known touch screen technologies include resistive touchscreens (a resistive contact layer allows the position of a pressure on the screen to be read); surface acoustic wave (SAW) technology (uses ultrasonic waves that pass over the touchscreen panel) to register the position of the touch event; capacitive (touching the surface changes capacitance); surface capacitance (change in the capacitance is measured from the four corners of the panel); optical or infrared sensors and LEDs mounted around a display (the sensors detecting a disruption in the pattern of LED beams); acoustic pulse recognition (tiny transducers attached to the edges of the touchscreen pick up the sound of the touch); Dispersive Signal Technology (DST, which consists of a chemically-strengthened glass substrate with piezos mounted on each corner to pinpoint the source of “bending waves” created by finger or stylus contact; and electromagnetic (change in magnetic flux is registered for the system to compute and define the coordinates of the touch event).
In measuring both the touch coordinates as well as the absolute amount of touch force, force-based touch screen technology such as F-Origin's zTouch™ has a great advantage in that software can ensure that the appropriate finger or stylus is touching the touch screen, and inadvertent pressures can be ignored. There have been a few attempts made to bridge this gap using other touch screen technologies. For example, Stantum™ is using a digital resistive solution that registers a larger touch area (multiple “interference points” in a coordinate grid). The software assumes that it is a finger that is touching the surface and the more touch points that are registering a touch, the larger the force is applied. Unfortunately, this logic fails if the user is using a finger nail or a stylus. Thus, for the time being, force-based touch screen technology retains its advantage. However, there are trade-offs. For example, force-based touch screen technology is only capable of discerning a single touch, and cannot differentiate two or more touches (“multi-touch”).
Indeed, all existing touch screen technologies come with a unique set of advantages and disadvantages, and so it is unlikely that any one will completely replace any other.
The most popular touch screen for mobile phones today is the Projective Capacitive (ProCap) touch screen. This technology supports multi-touch and will react to extremely light touches, however, it cannot measure force, nor can it recognize a touch from objects other than fingers or specialized styluses. The following table details the relative strengths and weaknesses of ProCap versus zTouch™ technologies.
FeatureProCapzTouch ™CombinedMulti touchYesNoYesForce SensingNoYesYes0-gram touchYesNoYesSettable touch thresholdsNoYesYesAny object touchNoYesYesUse with waterSomeYesYesUse with conductive gels/liquidsNoYesYesOptical impactSomeNoneSome
Clearly, the ideal solution combines the benefits of both. It would be advantageous to provide a hybrid touch-screen display that integrates force-based touch-screen technology with any one from among a group of projective capacitive, surface capacitive, resistive, digital resistive, SAW, IR, APR, DST, optical and electromagnetic touch-screen technologies. The “Combined” column in the table illustrates the benefits of a combined zTouch and ProCap solution discussed later in this document.